The present invention relates to a process and device for steering vehicle wheels rolling on test stands in order to determine vehicle behavior under actual operating conditions.
Among other things, vehicle test stands serve to examine, for example, the braking behavior of vehicles during the development and production stages. Moreover, such test stands, which can be designed with flat belt units or running drums, are used to measure the camber and track of the vehicle and also to test the behavior of the vehicle during actual operation. Also, these test stands are used to apply parameters previously ascertained on test runs, for example, pertaining to the spring deflection and swaying or shaking of a vehicle on the drive unit of the flat belt or drum-type test stand, in order to use the test stand to examine selected operating conditions of vehicles that have already been completed. Then, on the basis of these test results, the vehicles can be improved with respect to the anticipated conditions.
In order to be able to carry out such tests, it has been a known process to seat a driver in the vehicle, who then either motivates the test stand by means of the rolling wheels when the engine of the vehicle is running or else the driven test stand moves the wheels rolling on it without their being driven by the engine. It is also possible to employ a combination of both on these test stands whereby the test stand rollers or flat belts as well as the vehicle are driven.
Other possibilities for keeping a vehicle on the test stand while it is being tested are the so-called anchoring of the vehicle to the test stand, in other words, the chassis is anchored to the test stand or to the surrounding work area in such a manner that the vehicle cannot leave the test stand, even when improper loads are imposed.
Moreover, it is possible to use a steering system to keep the vehicle on track without a driver by guiding the vehicle's steering mechanism and thus to conduct test runs.
The measures described above to laterally hold the vehicle on test stands are also used for test stands where either only the steered axle of the vehicle or only the non-steered axle of the vehicle is in contact with a test stand. In this process, the vehicle can be driven on the test stand via the steered wheels or else via the non-steered wheels.
The above-mentioned steering systems correct the lateral motions of the vehicle by turning the vehicle's steering wheel. A familiar passive system consists in holding the steering wheel in an articulated manner by means of a rod or the like arranged perpendicular to the vehicle on a fixed point of the building or of the foundations so that the vehicle steers itself when it is moved, but only when no significant vertical forces occur in the test stand.
However, if great vertical forces occur in test stands, be it due to the superimposition of influencing variables in the horizontal direction or be it intentionally due to the exertion of additional vertical forces which, for example, simulate unevenness of a road surface--which generally stress each wheel differently and which are exerted onto the rolling wheels via the test stand rollers or flat belts--then great vertical motions are brought about in the vehicle. Among other things, swaying also occurs. In this context, swaying refers to a rolling motion of the vehicle by the length of one vehicle axis which, depending on the particular spring deflection of the vehicle wheels, generally moves away from its zero position. Due to these swaying motions, the rigid articulated rod leads to unnecessary motions of the steering wheel, a shifting of the vehicle away from its zero position and also to unstable steering. If the lateral shifting is prevented, for example, by a lateral anchoring or strapping of the vehicle, then inevitably constraining forces are exerted on the vehicle which can interfere with the test results.
The use of a driver entails additional costs and the measured results are influenced by the subjective handling of a situation by a human. Thus, questions arise whether the vehicles adjusted on the test stand in accordance with the particular vertical forces, that is to say, the riding comfort, can be reproducibly transferred to the actual driving behavior when the vehicle is driven on the open road.